The present invention relates in general to drive shields for use in tunnel-driving apparatus. More particularly, the invention is concerned with a drive shield composed of a plurality of elongate drive or cutter members arranged side-by-side and supported for displacement on a frame. Double-acting hydraulic rams serve selectively to advance the drive members and to draw up the frame.
Drive shield of the aforementioned kind are well known and are used for driving underground tunnels, adits galleries, roadways and the like. In such drive shields it is also known to construct the frame from two parts spaced apart along the tunnel. The rams are then positioned between the frame parts. It is however known from German published patent specifications 2622201 and 2849776, to construct the drive members as hollow components and to arrange the rams inside the drive members. The rams are thus held in a protected position and do not take up space within the shield. This arrangement permits the frame to be of moderate length. The rams are connected to the rear frame part with the aid of brackets.
In these known constructions the transmission of drive force to the rear frame part is problematic and it is difficult to gain access to the rams for replacement etc. in the restricted space available. There are also problems in attaching the so-called follow-up rear tails which extend the drive members in the rearward direction and enable a lining to be created behind the drive shield. Further difficulties can arise in the protection of the rams against the ingress of debris and dirt.
A general object of the present invention is to provide an improved drive shield construction.